Performance Problem with Clojure Array

Question

This piece of code is very slow. Execution from the slime-repl on my netbook takes a couple minutes.

(def test-array (make-array Integer/TYPE 400 400 3))

(doseq [x (range 400), y (range 400), z (range 3)]
   (aset test-array x y z 0))

Conversely, this code runs really fast:

(def max-one (apply max (map (fn [w] (apply max (map #(first %) w))) test-array)))
(def max-two (apply max (map (fn [w] (apply max (map #(second %) w))) test-array)))
(def max-three (apply max (map (fn [w] (apply max (map #(last %) w))) test-array)))

Does this have something to do with chunked sequences? Is my first example just written wrong?

dnolen · Accepted Answer · 2010-06-13 23:40:02Z

7

You're hitting Java reflection. This blog post has a workaround:

http://clj-me.cgrand.net/2009/10/15/multidim-arrays/

answered Jun 13, 2010 at 23:40

dnolen

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3 Comments

dbyrne Over a year ago

Thanks for the link. I thought it might be reflection, but I am not getting any reflection warnings? Any idea why not?

Michał Marczyk Over a year ago

Apparently *warn-on-reflection* doesn't always tell the whole story... See also clj-me.cgrand.net/2009/08/06/…

cgrand Over a year ago

With Clojure 1.2 you should get more reflection warnings on arrays.

Mars · Accepted Answer · 2013-11-05 03:13:44Z

0

You might get better performance from one of the four Clojure matrix implementations available via a single interface core.matrix: at clojars, at github.

answered Nov 5, 2013 at 3:13

Mars

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